1. Prior Art
Traditionally, a supplementary brake is provided in a large size motor vehicle in addition to a main brake for directly braking wheels. A hydrodynamic retarder is one kind of supplementary brake. In the field of this hydrodynamic retarder, the following art is published. Namely, the retarder is provided with a rotor wheel having blades and a stator wheel having blades. The rotor wheel is fixed to a driving shaft of a vehicle and is able to rotate. The stator wheel is fixed to a housing connected with a vehicle body. When the housing is filled with working oil, the working oil flows from the rotor side into the stator side with whirls colliding in the stator wheel so that a retardation or brake power is generated with the rotor wheel.
Moreover, Japanese publication No. 38-20510 or GB Patent No. 1,365,670 founded on U.S. Pat. No. 3,072,222, describe art which prevents air flowing into the stator wheel when the brake is empty of working oil. As a result, power output losses by air whirls are eliminated.
The Japanese art, however, requires a large shutter blade and an actuator to open and shut the blades. The GB Patent is provided with a device outside of a torus of the retarder.
2. Object of the Invention
An object of the present invention is to simplify a hydrodynamic retarder.
Another object is to provide a hydrodynamic retarder which will make it possible to eliminate the air whirl losses with a retarder empty of working fluid.